1. Field of the Invention
The present invention relates to an audio processing apparatus and an audio processing method which are preferably adapted to an audiovisual (AV) system. More particularly, the present invention is concerned with an audio processing technology preferably employed in a case where a system is constructed by connecting the audio processing apparatus to a television set or the like.
2. Description of the Related Art
The high-definition multimedia interface (HDMI) has prevailed as the specifications for transmission digital interfaces via which a video signal (image signal) and an audio signal are transmitted. The HDMI has been compiled by adding the specifications for an audio transmission facility and a copyright protection facility to the digital visual interface (DVI) specifications, which are the standard specifications for connection between a personal computer (PC) and a display, so that the specifications will apply to an audiovisual (AV) apparatus. In “High-definition Multimedia Interface Specification Version 1.3a” (Nov. 10, 2006) (non-patent document 1), the HDMI specifications are detailed.
Interfaces defined by the HDMI specifications can bi-directionally transmit a control signal. Therefore, for example, the control signal can be transmitted from a television set to an output apparatus such as a set-top box (STB) or a video disk player over an HDMI cable. Accordingly, an entire audiovisual system can be operated using a remote controller of the television set. Signals to be transmitted over a transmission cable defined by the HDMI specifications include control commands, which are used to a control apparatus, responses to the commands, and signals indicating the states of the apparatus. In this specification, the signals shall be generically called control signals.
The HDMI specifications support inter-apparatus control to be implemented using a consumer electronics control (CEC) facility. The CEC facility is one of transmission lines which are defined by the HDMI specifications and over which data is bi-directionally transmitted. The employment of the CEC line permits various controls to be implemented based on a physical address and a logical address inherently assigned to each of apparatuses interconnected on an HDMI network. For example, when a user is viewing a digital broadcast on a television set, if the user starts a video disk player connected over an HDMI cable, the television set autonomously selects an input terminal via which the video disk player is connected. In addition, the remote controller of the television set may be used to manipulate menu items displayed by the video disk player or turn on or off the power supply of the video disk player.
The HDMI specifications stipulate that up to ten apparatuses including a television set can be interconnected. This means that up to nine external apparatuses can be connected to one television set. When nine external apparatuses are connected to the television set, the remote controller can be used to operate any of the apparatuses.
The HDMI specifications define a message Active Source as a CEC message that explicitly indicates an apparatus whose image is displayed on a television set. According to the specifications, for example, when a user manipulates a reproduction button of a video disk player compatible with the HDMI specifications, the video disk player outputs an audiovisual stream as long as it can output a stable video signal (that is, when it is active). In addition, the video disk player broadcasts the message Active Source signifying that the video disk player is an active apparatus.
Now, “broadcasting” means that a signal is distributed to all apparatuses, which are transmission destinations, instead of being transmitted to any specific apparatus. The television set and other external apparatuses to which the message Active Source is broadcasted switch paths so as to reproduce an audiovisual stream to be outputted from the video disk player.
As mentioned above, the HDMI specifications stipulate that an apparatus which begins displaying a picture on the television set broadcasts the message Active Source to the other apparatuses on the network. The message Active Source is one of CEC messages defined by the HDMI specifications.
As described in JP-A-2008-35399 (patent document 1), a mode in which a reproductive sound field is changed from one to another according to genre information specified in an electronic program guide (EPG) received by a television set is realized as a CEC mode supported by the HDMI. In the mode, at the beginning of receiving a broadcast to be viewed on the television set, or when broadcasts are changed, the genre information specified in the EPG is transferred over a HDMI-CEC line. When an audio reproduction apparatus that may be called an audiovisual amplifier receives the genre information over the CEC line, the audio reproduction apparatus designates a reproductive sound field according to the genre information.
For example, when a sport program is viewed, a reproduction mode in which a sense of activity provided by the sport program is felt is designated. When a news program is viewed, a reproduction mode in which voice (speech) is readily heard is designated.